This invention relates to a system particularly for manufacturing hollow sections such as boards of a plastic material.
Prior art systems for manufacturing plastic material sections and panels are comprised of an extruder head for extruding the sections or panels and of a gauger or sizer, located downstream of said head and performing the functions of cooling the extruded section flowing out of the extruder head and of making it dimensionally stable. Such known systems, while generally successful, have proved in many instances deficient in versatility since, for example, when it was desired to change the shape or dimensions of the section or panel extruded from the head, it became necessary to replace as a whole the extruder head, thus adversely affecting the economy of the process, as an extensive range of extruder heads were required to meet the various market requirements.
Another strongly felt drawback resides in the gauger, i.e. in that part of the system which, as mentioned above, effectively controls the extruded section or panel dimensional stability. The gauger is comprised of a lower chamber and an upper chamber communicating to a vacuum source and closed, respectively, by a bottom plate and top plate which are caused to contact the lower and upper faces of the extruded section or panel and are effective to cool it gradually as well as to make the two faces of the section perfectly flat. Such plates are generally a single piece construction provided with a number of ports, in the form of holes or slots, for communicating to said upper and lower chambers. However, since as mentioned previously, said plates were a single piece construction, it happened that, owing to the high extruded section or panel temperature, thermal gradients occurred at the extruder head outlet between the various points in the plates; such thermal gradients, due to the unavoidable expansion of the plates, tended to distort the plates, which adversely affected the section finish.
Indeed, the plate internal stresses, as caused by the thermal gradient at the various points in the plates, resulted in a loss of flatness by the plates, such that the section or panel extruded by the extruder head was also affected, resulting in a loss of uniformity in the dimensional stability.